Blocking light, close and far
How Do Shadow Puppets Work?
A shadow is blocked light, and moving the hand nearer the light makes it enormous.
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Step 1 of 5
Light travels in straight lines.
It does not curve around obstacles. Anything solid in the way leaves a region behind it that light never reaches.
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Step 2 of 5
Light from a point spreads outward.
Rays fan out from a small source. The further they travel, the further apart they get.
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Step 3 of 5
So closer to the lamp means a bigger shadow.
A hand near the lamp blocks rays that would have spread far apart by the wall. Small movements change the size enormously.
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Step 4 of 5
A small source gives sharp edges.
One point source means one clean boundary. A large source lights the edge partly, blurring it into a soft fuzzy rim.
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Step 5 of 5
Turning the hand changes the outline.
Only the silhouette matters — the outline as seen from the lamp. That is why a small rotation turns a bird into a nonsense blob.
Shadow puppetry is over two thousand years old, and traditional performers use a single small flame for the sharpest edges.
The short version
Shadow puppets work because light travels in straight lines and spreads out, so hands nearer the lamp cast much larger shadows.
Try it yourself
Make a shadow on the wall, then move your hand halfway to the lamp without changing its shape. It doubles.
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